A known configuration of an illumination circuit of a discharge lamp (e.g., a metal halide lamp) includes a DC power supply circuit having a configuration of a DC-DC converter; a DC-AC conversion circuit (i.e., an inverter circuit); and a starter circuit (i.e., a starter). According to one such a configuration, a DC voltage from a battery is converted to a desired voltage in the DC power supply circuit, and is further converted to an AC output in the subsequent DC-AC conversion circuit. A start-up signal (a so-called starter pulse) is superposed thereon, and the superposed voltage is supplied to the discharge lamp (see, e.g., Japanese Patent Document JP-A-7-142182).
However, a configuration where a voltage is converted through two stages (i.e., a DC-DC voltage conversion and a DC-AC conversion) is not suitable for reducing the size of a circuit of large size. Therefore, there is used a configuration where an output—whose voltage has been boosted by a single-stage voltage conversion in a DC-AC conversion circuit—is supplied to a discharge lamp (see, e.g., Japanese Patent Document JP-A-7-169583)
Subsequently, a no-load output voltage (“OCV”) before the discharge lamp is illuminated (i.e., during an extinction period) is controlled so that a start-up signal is generated and supplied to the discharge lamp, there by causing the discharge lamp to illuminate. Thereafter, operation control (i.e., switching control) of the DC-AC conversion circuit is conducted to cause a transition to a steady illumination state.
A conventional illumination circuit may have problems. For example, a conventional illumination circuit may require a complicated control configuration for effecting a smooth and reliable transition of the discharge lamp to a steady illumination state.